A new University of Iowa study confirms what many women have long suspected -- that pregnancy permanently changes the size and shape of a woman's feet. Flat feet are a common problem for pregnant women. The arch of the foot flattens out, possibly due to the extra weight and increased looseness (laxity) of the joints associated with pregnancy. The new study, published in the March issue of the American Journal of Physical Medicine & Rehabilitation, suggests that this loss of arch height is permanent.